This invention relates generally to non-destructive testing and, more particularly, to ultrasound inspection of composite parts.
Ultrasonic inspection techniques are used in many applications where non-destructive evaluation of a workpiece is required. One application of such ultrasonic inspection is in the inspection of composite fiber reinforced aircraft engine fan blades. Such blades are typically formed from a plurality of layers of composite fibers (graphite, boron or S-glass, for example) laid over each other and adhesively bonded. Any separation of the fiber layers due to an incomplete bond or void in the blade may detrimentally affect blade strength. Ultrasonic inspection techniques can be used to identify and locate such flaws in a composite fiber reinforced blade. Additionally, ultrasound inspection techniques can be used to inspect composite aircraft engine parts, such as, but not limited to, composite ducts.
In the manufacture of composite materials, anomalous conditions may occur that impact the intended use of the composite material. Such conditions include but are not limited to porosity, delaminations, and foreign material. To detect these anomalous conditions, the composite materials are inspected using an ultrasonic nondestructive testing technique. If the ultrasonic test indicates that an anomalous condition exists, the size of the material anomaly needs to be measured accurately to make an engineering assessment of its impact on the intended use of the composite material.
Using at least some known test methods, the ultrasonic operator determines the boundary points of the material anomaly in the ultrasonic image using his/her best estimate based in the visual appearance of the image. Rules of thumb are typically used to facilitate determining the boundary of the indications. For example, a rule of thumb, such as, all points that are 2 times the mean amplitude of the image pixels surrounding the material anomaly in the image is used.
However such methods tend to reduce accuracy due to for example, a relatively large amount of measurement bias, which in some cases such bias can be approximately 50% of an actual size of the material anomaly. Additionally, such methods have relatively poor repeatability and reproducibility due to operator variability in making the measurements.